Spectral characteristics and Fresnel scale of high-latitude ionospheric scintillation

Abstract

Ionospheric scintillation refers to rapid fluctuations in the amplitude and phase of trans-ionospheric radio signals, caused by small-scale electron density irregularities. These fluctuations can disrupt signal tracking by Global Navigation Satellite System (GNSS) receivers, leading to positioning errors and degraded navigation performance. Understanding scintillation is essential for improving satellite-based positioning, navigation, and timing reliability and advancing the physical description of ionospheric plasma dynamics.

In the first part of this thesis, phase spectra characterized by a single power-law slope are analyzed using measurements from the Canadian High Arctic Ionospheric Network (CHAIN) GPS receivers. A systematic comparison between events with and without accompanying amplitude scintillation reveals a clear distinction: phase-only fluctuation events exhibit steeper spectral slopes, indicative of refractive effects produced by large-scale ionospheric structures, whereas events with both amplitude and phase scintillations display shallower slopes with enhanced high-frequency power, consistent with diffractive scattering by Fresnel-scale irregularities likely generated by gradient–drift instabilities.

In the second part, a two-component phase spectral model is introduced to characterize scintillation events within the auroral oval. The spectra consistently show a shallower slope at low frequencies and a steeper slope at high frequencies, revealing the coexistence of two distinct scattering regimes associated with different irregularity scale sizes. These results support a dual-mechanism interpretation of scintillation: large-scale refractive structures dominate phase fluctuations, while small scale diffractive irregularities produce amplitude scintillations. A power-law model of electron density turbulence successfully reproduces the observed two-slope behavior, underscoring the scale-dependent nature of ionospheric plasma structuring.

To further elucidate the origin of these spectral features, a numerical model of electromagnetic wave propagation through a refractive index field containing small-scale irregularities is developed. Using a Fourier spectral method under periodic boundary conditions, the simulation accurately resolves the evolution of log-amplitude and phase along the propagation direction. By reducing the problem from three to two dimensions while retaining key diffraction physics, the model reproduces realistic scintillation patterns and demonstrates how anisotropic wave propagation and scale coupling govern the observed spectral behavior.